There are in existence several systems for detecting or preventing the theft of articles of value. One of these corresponds to U.S. Pat. No. 3,292,080 granted to E. M. Trikilis on Dec. 13, 1966 which makes use of a magnetometer and utilizes a magnetized object which identifies the article unless check-out procedure has removed the magnetism from the object.
Another system involves radioactive material which emits nuclear radiation. When the label containing the magnetic material is removed from the merchandise, the radiation is no longer emitted, and therefore radiation detectors situated in the doorway are not energized. On the other hand, if the radiation emitters remain on the merchandise, doorway sensors of nuclear radiation react, and security personnel are in a position to prevent the theft. However, there are severe health problems with this system involving danger to people from the nuclear radiation.
A further system involves the use of a radio frequency generating device imbedded in a rubber pad. The radio frequency emitting device is fastened to articles and if not removed will energize radio frequency detecting antenna at the doorway. In the normal course of events, when the merchandise is sold, a special fastener is unlocked and the radio frequency emitter is removed from the clothing at the time it is sold, permitting the buyer to pass through the doorway without attracting the attention of the store detectives. However, this system is extremely costly and is therefore undesirable.
The following United States patents illustrate a number of alternative proposals which will serve as background to the invention described and illustrated herein namely:
U.S. Pat. No. 3,631,442; PA1 U.S. Pat. No. 3,747,086; PA1 U.S. Pat. No. 3,754,226; PA1 U.S. Pat. No. 3,790,945; PA1 U.S. Pat. No. 3,820,103.